Tone sustaining system for electric musical instrument



March 14, 1967 D. M. PARK 3,309,453

TONE SUSTAI N ING SYSTEM FOR ELECTRIC MUSICAL INSTRUMENT Filed J-une 15, 1964 3 Sheets-Sheet 1 DC VOLTAGE I VOLTAGE I 220 I E L: SUPPLY DIVIDER I r- 53' 10 A FREQUINCY PEDAL OPERATED /4o 52 SWITCH STABILIZER l LOW I IMPEDANCE J50 SHORT RC MEMORY TIME PATH v I5 I v I-IIGI-I IMPEDANCE LONGRC PULSE 9 TIME PATHS OSCILLATOR K I I I KEYER /72 PEDAL CLAVIER AMPLIFIER SPEAKER FIG. I.

INVENTOR. Donald M. P rk March 14, 1967 FOTENTTA'L.

AMPUTUDE TONE SUS Filed June 15, 1964 D. M. PARK 3,309,453

TAINING SYSTEM FOR ELECTRIC MUSICAL INSTRUMENT 3 Sheets-Sheet 3 STEAOY STATE 20o VOLTAGE AT INT v A CUT OPP VOLT/xiv" B 100 AT POM v To 7 1 2 3 4 T5 T6 T7 TIME c PULSE IHH 1| mmnmmmmmmmmum!1m OUTPUT OUTPUT INTEGRATOR OUTPUT I -AUDlO VSUSTAINED KEYER OUTPUT T0 T1 T T 5 6 7 TIME FIGS INVENTOR.

' Donald M. Park BY fififig ATTORNEY United States Patent 3,309,453 TONE SUSTAINING SYSTEM FOR ELECTRIC MUSICAL INSTRUMENT Donald M. Park, Raleigh, N.C., assignor to Park-Baker Electronic Development Corporation, Raleigh, N.C., a corporation of North Carolina Filed June 15, 1964, Ser. No. 375,095 1 Claim. (Cl. 841.13)

This invention relates generally to electric musical instruments, and more particularly, to tone sustaining sys term for electric musical instruments wherein the frequency of a decaying tone is held constant.

Conventional electronic organs include a plurality of tone generators, usually in the form of oscillators, which are coupled to an audio system through appropriate gates controlled by the organ keys. The tone generating oscillators are generally coupled together with the output signal of the first oscillator being fed into the second oscil-' lator, the output signal of the second oscillator being fed into the third oscillator, and so forth throughout the entire series of oscillators. The series of oscillators acts as a sequential frequency dividing network so that each oscillator produces a tone signal at half the frequency of the preceding oscillator, thereby producing a scale of notes. Other prior art systems have also employed a series of oscillators even though not in the same sequential frequency array. In any event, compared to the described conventional circuitry, the circuitry of the present invention obtains different tones through a tone generator having a voltage responsive oscillator whose output frequency is governed by the voltage applied to the input of the oscillator. That is, the circuitry of the present invention is built around employment of a tone generator having a voltage responsive pulse oscillator such that a plurality of control members can gain a plurality of tones from a single tone generator by having each control mem: ber arranged to establish a particular control voltage corresponding to a particular tone.

Operation of any electric organ, whether of the type having a series of oscillators or of the voltage responsive oscillator type, by a player is eifected by manual and foot operation of keyboard control members such as keys, claviers and pedals. Each of these control members actually produces an electrical control pulse each time it is moved, so that the frequency of operation of these members actually sets the tempo at which the organ is played. In addition to controlling the frequency or tempo of the organ, the control members also control the tone produced by the organ, i.e., each key, clavier or pedal actually controls a different tone. It is desirable to have a particular tone continue to be produced or sustained for a short period of time after a key, clavier or pedal is released from its operating position without the tone having a detectable change in frequency. Some sort of memory device is generally associated with each control member in order to sustain the tone controlled by that member for a desired decay time. A number of different memory devices have been proposed for sustaining such tones in prior art musical instruments but all of the devices pro-v posed heretofore have either been relatively complex or costly or have had an undesirable frequency drift after a period of time in operation.

It is therefore the main object of this invention to pro- Vide a tone circuit having improved tone sustaining for use in electric organs or other electrical musical instruments.

Another object of this invention is to provide a simplified tone circuit for electric organs and the like in which the tone is sustained at a substantially constant frequency as it decays following employment of a control member.

3,309,453 7 Patented Mar. 14, 1967 The foregoing 'as well as other objects and advantages inherent in theinvention will become more apparent from the following description of a suitable embodiment of the invention shown in the accompanying drawings.

In the drawings:

FIGURE 1 is a block diagram of a musical instrument circuit embodying the invention.

FIGURE 2 is a schematic diagram of the circuit of FIGURE 1.

FIGURE 3 compares in a single figure with respect to a common time axis certain relevant voltage and pulse waves found in the circuitry of FIGURES 1 and 2.

Considering the invention circuitry in block diagram form, reference is first made to FIGURE 1 showing an embodiment of the invention applied to an electric organ. In FIGURE 1 a DC. voltage supply 10 is connected to-a voltage responsive tone generator 60, comprised of a voltage responsive high impedance, pulse oscillator 67 and a complementary flip-flop 68, the connection being made through a path which includes a voltage divider 20, a pedal operated switch 40, a memory and an adjustable resistor which provides a fine tone adjustment for the tone generator 60. The DC. voltage supply 10 is also connected to the tone generator by another path 53 in series with resistor 55 and which includes a resistor 52. Path 53 and resistor 52, as later explained, provide a frequency stabilizer circuit.

Tone generator 60 is connected to a keyer 72 through an integrator 70, and the keyer is connected to a speaker 76 through an amplifier 74. A pedal clavier 78 is operatively connected to the keyer 72 and the pedal operated switch 40.

The integrator 70, the flip-flop 68, the keyer 72, the amplifier 74, the speaker 76 and the pedal clavier 78 are well known in the art and will not be described further. In the more detailed description now following, emphasis is given to other components having a more direct bearing on the invention.

Referring to the circuit diagram of FIGURE 2, the voltage divider 20 is comprised of a resistor 16, a plurality of resistors indicated by 17, and voltage regulator diodes 11, 12, 13 and 14. Though two diodes 13 and 14 are shown and their values mentioned later, a single diode of equivalent value could be used. The voltage divider 20 1s connected from a point Z to a point X in the tone generator 60 through a resistor 18 and three neon glow tubes indicated by 19. Though three neon tubes 19 are shown, they could be replaced by one of equivalent value. Point Y in the voltage divider 20 is connected to point X of the tone generator 60 through a diode 15 and neon tubes 19.

The voltage divider 20 is operatively connected by another path to the tone generator 60 through the pedal clavier operated switch 40, comprised of a plurality of individually operated switches 31, 32, 33, 34, 41, 42, 43, 44, 45, 46, 47, 48, 49, and then through the variable resistor 55 to a point T. The referred to switches together with the related manual operating devices such as pedal claviers serve to control members connected to the voltage divider 20 for actuating the tone generator '60.

The DC. voltage supply 10 is connected to the tone generator 60 at the same point T through the fixed resistor 52, which provides the previously mentioned frequency stabilizing circuit, and the variable resistor .55.

The voltage responsive pulse oscillator 67 which is a part of the tone generator 60 is comprised of a resistor 61, a neon glow tube 62, a resistor 66 and capacitors 63, 64 and 65. Capacitors 64 and 63 are arranged as a voltage divider to electrically isolate feedback from the flip-flop 68. Other types of high impedance oscillators could be employed.

Referring to FIGURE 3, certain pertinent wave and pulse shapes are compared on a common time axis. Line 100 represents the cut-off voltage of the tone generator 60, below this input voltage level there is no output from the tone generator. Line 200 represents the voltage level present at the input point V of the tone generator when the pedal operated switch 40 is in the open position after a relatively long time. Curve A represents the voltage present at the input point V of the tone generator prior to, during, and after a pedal is played. Curve B represents the voltage decay present at the input point V of tone generator 60 without the frequency stabilizing circuit provided by path 51 and resistor 52. That is, curve B shows how curve A would appear without the effect of path 53 and resistor 52.

T represents the time when the pedal clavier 78 and a switch 41 are connected. T represents the time when the pedal clavier 78 and switch 41 are later disconnected. Tg-Tq are RC time constant intervals of the equivalent RC circuit when the pedal clavier 78 and the pedal operated switch 40 are disconnected.

Curves C, D and E represent respectively the output of the pulse oscillator 67, the flip-flop 68 and the integrator 70. Curve F represents the frequency characteristic of the keyer 72 output and curve G represents the amplitude envelope characteristic of the output keyer 72. T and T are as described above and T as a general example, is the time after which the keyer 72 will not longer have an audible output.

Considering the circuit functions, in the voltage divider 20 resistors 16 and 17 are of such value as to present the desired voltage to a particular control member switch, such as 41, when the corresponding foot pedal, not shown, operates the pedal clavier 78, which in turn operates the particular switch. Ideally under steady state conditions point W and point V should be at the same potential which is the same as curve A at steady state. Diodes 11, 12, 13 and 14 give a low impedance path during the time when the capacitor 51 is charging due to a control member, such as switch 41, being closed, An important aspect of the circuit being described is that capacitor 51 charges very rapidly due to a low RC time constant when any of of the switches in switch 40 are closed but discharges slowly due to a relatively high RC time constant which prevails as to capacitor 51 after switch 40 is opened.

Diode 15 serves to help start the neon tubes 19 by affording a low impedance path to point Y after the tubes 19 fire. Resistor 18 provides an alternate path to a higher than normal voltage source in order to facilitate initial ionization of tubes 19. The neon tubes 19 themselves are used to place a potential at point X. The circuit employing the neon tubes is in fact in the nature of a feedback circuit in that variations in the voltage supply which would produce a variation of voltage at point T will also produce a corresponding variation of voltage at point X, therefore insuring that the long term potential between point T and point X will remain correct regardless of voltage supply 10 variations. Stated differently, this feedback circuit presents a specific potential to one side of the oscillator which is a function of variations in the voltage divider source potential and is adjusted to maintain a long term frequency stability.

The pulse oscillator 67 is a normally operative relaxation oscillator whose frequency is determined by the potential between points V and X. The voltage at input V can be greater or less than the steady state voltage 200 depending on whether a switch such as switch 41 is closed which gives a greater voltage whereas a switch such as switch 34 would give a lesser voltage. FIGURE 3 uses a greater voltage as an example. In any event each switch such as switch 41 establishes its own particular voltage at V and accordingly establishes its own particular tone.

In normal operation with the pedal operated switch open for a long time, a steady state voltage, represented by the extreme left portion of curve A and line 200, is present at point V. This voltage 200 causes the pulse 4, oscillator 67 to operate steadily at a certain frequency, for reference purposes called F The output of the pulse generator cannot pass the keyer 72, for the keyer only operates while the pedal clavier 78 is connected and for a short time after the pedal clavier is disconnected.

When a foot pedal, not shown, connected to the pedal clavier 78 is depressed, switch 41 is closed and the pedal clavier 78 activates the keyer 72. T T represents the time when thte switch 41 is closed. It can be seen that the voltage at the input V of the tone generator 60 represented by curve A is now different from the steady state voltage 200. As previously mentioned, the voltage at V can be either above or below voltage 200 depending on which switch has been closed. This increased voltage causes the frequency in the example chosen, for reference called F of the tone generator to increase, and this signal is passed to and through the keyer 72 into the amplifier 74 and speaker 76.

It may be noted that in a circuit without the frequency stabilizing circuit formed by path 53 and resistor 52, when the switch 41 is opened the memory device 50 will start to discharge toward a zero potential. The voltage B at point V would change correspondingly thereby changing the frequency of the tone generator 60. When the voltage B falls below line the tone generator 60 ceases to operate. This objectionable rapid change in frequency is readily discernable in the audio output it the tone is sustained.

With the frequency stabilizing circuit formed by path 53 and resistor 52, when the switch 41 is opened the voltage A at the input V decreases in a much slower manner since the memory 50 discharges toward a higher potential 200. This slower change in voltage A creates a correspondingly slower change in the output frequency of the tone generator 60. The tone can thus be sustained for a longer period of time without having an audibly detectable change in frequency which as previously stated is most undesirable. The keyer 72 is designed in the example shown, to cut off at time T therefore prohibiting any detectable frequency change from passing with a particular tone after time T As previously stated, the voltage at point V can be greater or less than the steady state voltage 200 depending on which of control switches 31-49 are closed. Thus, if a switch 34 were closed a lower voltage than normal would be at point V, thereby causing the tone generator 60 to operate at a lower frequency, for reference called F When the switch 34 is opened the tone generator frequency will change toward P For a short period of time no discernible change in frequency can be detected, thereby allowing the tone to be sustained without having an undesirable detectable frequency shift.

The following constants which have been used in the circuit of FIGURE 2 are listed below merely by way of illustration and are not intended to limit the scope of the invention in any Way:

Voltage supply 10, DC. volts 365 Diode 11 10T47 Diode 12 10T62 Diode 13 10Tl00 Diode 14 10T7S Diode 15 1N3254 Resistor 16, kilohms 3 Resistors 17, kilohms 1 Resistor 18, megohms 4.7 Neon tubes 19 Ne 23 Capacitor 51, microfarads 4 Resistor 52, megohms 10 Resistor 55, megohms (adjustable) 0-5 Resistor 61, megohms l0 Neon tube 62 Ne 23 Capacitor 63, microfarad .l Capacitor 64, microfarad .004 Capacitor 65, microfarad l .002 Resistor 66, kilohrns 24 In summary, the invention is built around the concept of. utilizing a single voltage responsive pulse oscillator to provide a range of frequencies for a manually operated keyboard e.g. a pedal keyboard and with a memory circuit for sustaining each played frequency constant as it decays to an inaudible sound. Each control member when operated connects the continuously operative oscillater to a particular voltage level either above or below the steady state voltage level. The particular voltage level obtained by the control member is obtained at point V almost instantaneously from the voltage divider due to a low impedance path with a short RC time constant (made up of applicable resistors 17 and capacitor 51) being placed in parallel with a high impedance path having a high RC time constant (made up of capacitor 51 and the resistor equivalent of those resistors tied to point V). Simultaneous with obtaining the particular voltage level at point V, keyer 72 passes the corresponding tone frequency to the amplifier 74. When the control member (such as switch 41 operated by pedal clavier 78) is disconnected only the high impedance, high RC time constant path is operative and the memory 50 acts to maintain the last obtained particular voltage level and in doing so maintains the last played frequency constant until it becomes inaudible or until a new frequency replaces the last played frequency.

Having described the invention, I claim:

In an electric organ, a tone circuit comprised of (a) a direct current voltage source;

(b) a normally operating tone generator having a voltage responsive pulse oscillator connected to and driven by a steady state voltage obtained from said source;

(c) a voltage divider connected to said source;

(d) a keyer connected to the output of said tone generator;

(e) a keyboard having manually operated played control members operatively connected to said divider and said keyer, each said control member being adapted to open said keyer and connect a particular voltage point on said divider with said oscillator whereby to drive said oscillator with said particular a voltage obtained from said divider thereby causing a tone of frequency corresponding to said particular voltage to pass said keyer;

(f) circuit means providing a high impedance in the path between said source and oscillator and a low impedance in the path between said divider and oscillator and including a memory connected between said divider and oscillator, said memory being operative when a said control member is closed to rapidly rise or fall from said steady state voltage to said particular voltage and when the same said control member is subsequently opened to hold the said particular voltage so obtained substantially constant while said particular tone decays thereby sustaining the frequency of said particular tone during said decay; and

g) including a feedback circuit between said oscillator and divider and so connected as to provide on one side of said oscillator a voltage which varies as the source voltage varies whereby to maintain a long term frequency stability.

References Cited by the Examiner UNITED STATES PATENTS 4/1965 Harmon 84-126 6/1965 Anderson 84-l.13 

